A device for separating foreign particles out of a cooling-air stream which for cooling purposes is fed to a turbine rotor blade, preferably of a gas turbine installation, of the generic type is known from EP 0 690 202 B1. In the known case, cooling air is fed via stationary swirl nozzles to an annular space, which is delimited between wall parts of the turbine stator and a rotor disk, to form a turbulent flow that propagates in the circumferential direction within the annular space. The swirl nozzles each have a tangential orientation in the circumferential direction of their arrangement within the turbine stator, with the individual nozzle axes in the respective tangential plane being set obliquely with respect to the axis of rotation of the rotor arrangement, in order to form a swirling flow within the annular space.
A metal diverter plate, which is L-shaped in cross-section, is provided inside the annular space, immediately downstream of the swirl nozzles, as seen in the direction of flow; the cooling air, on emerging from the swirl nozzles, impinges perpendicularly on the longer longitudinal limb of this diverter plate, which is preferably oriented radially with respect to the rotor arrangement, and is diverted radially outward. For design reasons, the diverter plate provides, on the radially inner side with respect to the outlet opening of the swirl nozzles, a flow dead space in which foreign particles inevitably accumulate, preferably through accumulation of relatively heavy and/or large foreign particles. Deposits of this nature on the surface of the radially inner, shorter L limb lead to a risk of contamination to the cooling-air stream that forms in the annular space which should not be underestimated yet to which it is quite obvious that no further attention is paid in the above-mentioned document.
Moreover, the same document reveals a further exemplary embodiment, in which an L-shaped part, which is formed with an acute angle in cross-section, is used as the metal diverter plate, with the cooling-air stream that emerges from the swirl nozzles impinging at an angle on the longer L-limb of the diverter plate; this angle causes the cooling-air stream to be at least partially deflected radially inward. In this case, it can be assumed that the deposition of foreign particles described above will occur to an even greater extent than in the first case described.
A further device for removing dust particles from the cooling air of a gas turbine is disclosed by EP 1 174 589 A1. In the case outlined above, as it were, wall parts of the guide vane and rotor blade, positioned axially opposite one another, of a rotor arrangement delimit a type of annular space into which a cooling-air stream is introduced as swirling stream. The foreign particle separation is performed in such a manner that the cooling air that emerges from a first nozzle arrangement impinges on a type of diverter unit, by means of which the cooling-air stream is divided into a partial air stream that is directed radially outward and a partial air stream that is directed radially inward. By providing certain flow links, the radially outwardly directed partial air stream, which has increased levels of foreign particles, is passed radially outward into the hot-gas stream of the gas turbine. The accumulation of foreign particles in the radially outwardly directed partial air stream originates from the centrifugal force that acts on the foreign particles and forms as a result of the swirling flow propagating in the circumferential direction after it has passed through the swirl nozzle openings. Although it is possible to separate out relatively high-mass foreign particles using the separation method described in this document, it is impossible to rule out lightweight and smaller dust or foreign particles being entrained by the radially inwardly directed cooling-air stream for further cooling of the turbine rotor blade.